/*
  Copyright 2014 Google Inc.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

// Windows Timer Primer
//
// A good article:  http://www.ddj.com/windows/184416651
// A good mozilla bug:  http://bugzilla.mozilla.org/show_bug.cgi?id=363258
//
// The default windows timer, GetSystemTimeAsFileTime is not very precise.
// It is only good to ~15.5ms.
//
// QueryPerformanceCounter is the logical choice for a high-precision timer.
// However, it is known to be buggy on some hardware.  Specifically, it can
// sometimes "jump".  On laptops, QPC can also be very expensive to call.
// It's 3-4x slower than timeGetTime() on desktops, but can be 10x slower
// on laptops.  A unittest exists which will show the relative cost of various
// timers on any system.
//
// The next logical choice is timeGetTime().  timeGetTime has a precision of
// 1ms, but only if you call APIs (timeBeginPeriod()) which affect all other
// applications on the system.  By default, precision is only 15.5ms.
// Unfortunately, we don't want to call timeBeginPeriod because we don't
// want to affect other applications.  Further, on mobile platforms, use of
// faster multimedia timers can hurt battery life.  See the intel
// article about this here:
// http://softwarecommunity.intel.com/articles/eng/1086.htm
//
// To work around all this, we're going to generally use timeGetTime().  We
// will only increase the system-wide timer if we're not running on battery
// power.  Using timeBeginPeriod(1) is a requirement in order to make our
// message loop waits have the same resolution that our time measurements
// do.  Otherwise, WaitForSingleObject(..., 1) will no less than 15ms when
// there is nothing else to waken the Wait.

#include "base/time.h"

#pragma comment(lib, "winmm.lib")
#include <windows.h>
#include <mmsystem.h>

#include "base/basictypes.h"
#include "base/logging.h"
#include "base/cpu.h"
#include "base/singleton.h"
#include "base/synchronization/lock.h"

using base::Time;
using base::TimeDelta;
using base::TimeTicks;

namespace {

// From MSDN, FILETIME "Contains a 64-bit value representing the number of
// 100-nanosecond intervals since January 1, 1601 (UTC)."
int64 FileTimeToMicroseconds(const FILETIME& ft) {
  // Need to bit_cast to fix alignment, then divide by 10 to convert
  // 100-nanoseconds to milliseconds. This only works on little-endian
  // machines.
  return bit_cast<int64, FILETIME>(ft) / 10;
}

void MicrosecondsToFileTime(int64 us, FILETIME* ft) {
  DCHECK_GE(us, 0) << "Time is less than 0, negative values are not "
      "representable in FILETIME";

  // Multiply by 10 to convert milliseconds to 100-nanoseconds. Bit_cast will
  // handle alignment problems. This only works on little-endian machines.
  *ft = bit_cast<FILETIME, int64>(us * 10);
}

int64 CurrentWallclockMicroseconds() {
  FILETIME ft;
  ::GetSystemTimeAsFileTime(&ft);
  return FileTimeToMicroseconds(ft);
}

// Time between resampling the un-granular clock for this API.  60 seconds.
const int kMaxMillisecondsToAvoidDrift = 60 * Time::kMillisecondsPerSecond;

int64 initial_time = 0;
TimeTicks initial_ticks;

void InitializeClock() {
  initial_ticks = TimeTicks::Now();
  initial_time = CurrentWallclockMicroseconds();
}

}  // namespace

// Time -----------------------------------------------------------------------

// The internal representation of Time uses FILETIME, whose epoch is 1601-01-01
// 00:00:00 UTC.  ((1970-1601)*365+89)*24*60*60*1000*1000, where 89 is the
// number of leap year days between 1601 and 1970: (1970-1601)/4 excluding
// 1700, 1800, and 1900.
// static
// const int64 Time::kTimeTToMicrosecondsOffset = GG_INT64_C(11644473600000000);
const int64 Time::kTimeTToMicrosecondsOffset = GG_LONGLONG(11644473600000000);

bool Time::high_resolution_timer_enabled_ = false;

// static
Time Time::Now() {
  if (initial_time == 0)
    InitializeClock();

  // We implement time using the high-resolution timers so that we can get
  // timeouts which are smaller than 10-15ms.  If we just used
  // CurrentWallclockMicroseconds(), we'd have the less-granular timer.
  //
  // To make this work, we initialize the clock (initial_time) and the
  // counter (initial_ctr).  To compute the initial time, we can check
  // the number of ticks that have elapsed, and compute the delta.
  //
  // To avoid any drift, we periodically resync the counters to the system
  // clock.
  while (true) {
    TimeTicks ticks = TimeTicks::Now();

    // Calculate the time elapsed since we started our timer
    TimeDelta elapsed = ticks - initial_ticks;

    // Check if enough time has elapsed that we need to resync the clock.
    if (elapsed.InMilliseconds() > kMaxMillisecondsToAvoidDrift) {
      InitializeClock();
      continue;
    }

    return Time(elapsed + Time(initial_time));
  }
}

// static
Time Time::NowFromSystemTime() {
  // Force resync.
  InitializeClock();
  return Time(initial_time);
}

// static
Time Time::FromFileTime(FILETIME ft) {
  return Time(FileTimeToMicroseconds(ft));
}

FILETIME Time::ToFileTime() const {
  FILETIME utc_ft;
  MicrosecondsToFileTime(us_, &utc_ft);
  return utc_ft;
}

// static
void Time::EnableHighResolutionTimer(bool enable) {
  // Test for single-threaded access.
  static PlatformThreadId my_thread = PlatformThread::CurrentId();
  DCHECK(PlatformThread::CurrentId() == my_thread);

  if (high_resolution_timer_enabled_ == enable)
    return;

  high_resolution_timer_enabled_ = enable;
}

// static
bool Time::ActivateHighResolutionTimer(bool activate) {
  if (!high_resolution_timer_enabled_)
    return false;

  // Using anything other than 1ms makes timers granular
  // to that interval.
  const int kMinTimerIntervalMs = 1;
  MMRESULT result;
  if (activate)
    result = timeBeginPeriod(kMinTimerIntervalMs);
  else
    result = timeEndPeriod(kMinTimerIntervalMs);
  return result == TIMERR_NOERROR;
}

// static
Time Time::FromExploded(bool is_local, const Exploded& exploded) {
  // Create the system struct representing our exploded time. It will either be
  // in local time or UTC.
  SYSTEMTIME st;
  st.wYear = exploded.year;
  st.wMonth = exploded.month;
  st.wDayOfWeek = exploded.day_of_week;
  st.wDay = exploded.day_of_month;
  st.wHour = exploded.hour;
  st.wMinute = exploded.minute;
  st.wSecond = exploded.second;
  st.wMilliseconds = exploded.millisecond;

  // Convert to FILETIME.
  FILETIME ft;
  if (!SystemTimeToFileTime(&st, &ft)) {
    NOTREACHED() << "Unable to convert time";
    return Time(0);
  }

  // Ensure that it's in UTC.
  if (is_local) {
    FILETIME utc_ft;
    LocalFileTimeToFileTime(&ft, &utc_ft);
    return Time(FileTimeToMicroseconds(utc_ft));
  }
  return Time(FileTimeToMicroseconds(ft));
}

void Time::Explode(bool is_local, Exploded* exploded) const {
  // FILETIME in UTC.
  FILETIME utc_ft;
  MicrosecondsToFileTime(us_, &utc_ft);

  // FILETIME in local time if necessary.
  BOOL success = TRUE;
  FILETIME ft;
  if (is_local)
    success = FileTimeToLocalFileTime(&utc_ft, &ft);
  else
    ft = utc_ft;

  // FILETIME in SYSTEMTIME (exploded).
  SYSTEMTIME st;
  if (!success || !FileTimeToSystemTime(&ft, &st)) {
    NOTREACHED() << "Unable to convert time, don't know why";
    ZeroMemory(exploded, sizeof(exploded));
    return;
  }

  exploded->year = st.wYear;
  exploded->month = st.wMonth;
  exploded->day_of_week = st.wDayOfWeek;
  exploded->day_of_month = st.wDay;
  exploded->hour = st.wHour;
  exploded->minute = st.wMinute;
  exploded->second = st.wSecond;
  exploded->millisecond = st.wMilliseconds;
}

// TimeTicks ------------------------------------------------------------------
namespace {

// We define a wrapper to adapt between the __stdcall and __cdecl call of the
// mock function, and to avoid a static constructor.  Assigning an import to a
// function pointer directly would require setup code to fetch from the IAT.
DWORD timeGetTimeWrapper() {
  return timeGetTime();
}

DWORD (*tick_function)(void) = &timeGetTimeWrapper;

// Accumulation of time lost due to rollover (in milliseconds).
int64 rollover_ms = 0;

// The last timeGetTime value we saw, to detect rollover.
DWORD last_seen_now = 0;

// Lock protecting rollover_ms and last_seen_now.
// Note: this is a global object, and we usually avoid these. However, the time
// code is low-level, and we don't want to use Singletons here (it would be too
// easy to use a Singleton without even knowing it, and that may lead to many
// gotchas). Its impact on startup time should be negligible due to low-level
// nature of time code.
base::Lock rollover_lock;

// We use timeGetTime() to implement TimeTicks::Now().  This can be problematic
// because it returns the number of milliseconds since Windows has started,
// which will roll over the 32-bit value every ~49 days.  We try to track
// rollover ourselves, which works if TimeTicks::Now() is called at least every
// 49 days.
TimeDelta RolloverProtectedNow() {
  base::AutoLock locked(rollover_lock);
  // We should hold the lock while calling tick_function to make sure that
  // we keep last_seen_now stay correctly in sync.
  DWORD now = tick_function();
  if (now < last_seen_now)
    rollover_ms += 0x100000000I64;  // ~49.7 days.
  last_seen_now = now;
  return TimeDelta::FromMilliseconds(now + rollover_ms);
}

// Overview of time counters:
// (1) CPU cycle counter. (Retrieved via RDTSC)
// The CPU counter provides the highest resolution time stamp and is the least
// expensive to retrieve. However, the CPU counter is unreliable and should not
// be used in production. Its biggest issue is that it is per processor and it
// is not synchronized between processors. Also, on some computers, the counters
// will change frequency due to thermal and power changes, and stop in some
// states.
//
// (2) QueryPerformanceCounter (QPC). The QPC counter provides a high-
// resolution (100 nanoseconds) time stamp but is comparatively more expensive
// to retrieve. What QueryPerformanceCounter actually does is up to the HAL.
// (with some help from ACPI).
// According to http://blogs.msdn.com/oldnewthing/archive/2005/09/02/459952.aspx
// in the worst case, it gets the counter from the rollover interrupt on the
// programmable interrupt timer. In best cases, the HAL may conclude that the
// RDTSC counter runs at a constant frequency, then it uses that instead. On
// multiprocessor machines, it will try to verify the values returned from
// RDTSC on each processor are consistent with each other, and apply a handful
// of workarounds for known buggy hardware. In other words, QPC is supposed to
// give consistent result on a multiprocessor computer, but it is unreliable in
// reality due to bugs in BIOS or HAL on some, especially old computers.
// With recent updates on HAL and newer BIOS, QPC is getting more reliable but
// it should be used with caution.
//
// (3) System time. The system time provides a low-resolution (typically 10ms
// to 55 milliseconds) time stamp but is comparatively less expensive to
// retrieve and more reliable.
class HighResNowSingleton {
 public:
  static HighResNowSingleton* GetInstance() {
    return Singleton<HighResNowSingleton>::get();
  }

  bool IsUsingHighResClock() {
    return ticks_per_microsecond_ != 0.0;
  }

  void DisableHighResClock() {
    ticks_per_microsecond_ = 0.0;
  }

  TimeDelta Now() {
    if (IsUsingHighResClock())
      return TimeDelta::FromMicroseconds(UnreliableNow());

    // Just fallback to the slower clock.
    return RolloverProtectedNow();
  }

  int64 GetQPCDriftMicroseconds() {
    if (!IsUsingHighResClock())
      return 0;

    return abs((UnreliableNow() - ReliableNow()) - skew_);
  }

 private:
  HighResNowSingleton()
    : ticks_per_microsecond_(0.0),
      skew_(0) {
    InitializeClock();

    // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is
    // unreliable.  Fallback to low-res clock.
    base::CPU cpu;
    if (cpu.vendor_name() == "AuthenticAMD" && cpu.family() == 15)
      DisableHighResClock();
  }

  // Synchronize the QPC clock with GetSystemTimeAsFileTime.
  void InitializeClock() {
    LARGE_INTEGER ticks_per_sec = {0};
    if (!QueryPerformanceFrequency(&ticks_per_sec))
      return;  // Broken, we don't guarantee this function works.
    ticks_per_microsecond_ = static_cast<float>(ticks_per_sec.QuadPart) /
      static_cast<float>(Time::kMicrosecondsPerSecond);

    skew_ = UnreliableNow() - ReliableNow();
  }

  // Get the number of microseconds since boot in an unreliable fashion.
  int64 UnreliableNow() {
    LARGE_INTEGER now;
    QueryPerformanceCounter(&now);
    return static_cast<int64>(now.QuadPart / ticks_per_microsecond_);
  }

  // Get the number of microseconds since boot in a reliable fashion.
  int64 ReliableNow() {
    return RolloverProtectedNow().InMicroseconds();
  }

  // Cached clock frequency -> microseconds. This assumes that the clock
  // frequency is faster than one microsecond (which is 1MHz, should be OK).
  float ticks_per_microsecond_;  // 0 indicates QPF failed and we're broken.
  int64 skew_;  // Skew between lo-res and hi-res clocks (for debugging).

  friend struct DefaultSingletonTraits<HighResNowSingleton>;
};

}  // namespace

// static
TimeTicks::TickFunctionType TimeTicks::SetMockTickFunction(
    TickFunctionType ticker) {
  TickFunctionType old = tick_function;
  tick_function = ticker;
  return old;
}

// static
TimeTicks TimeTicks::Now() {
  return TimeTicks() + RolloverProtectedNow();
}

// static
TimeTicks TimeTicks::HighResNow() {
  return TimeTicks() + HighResNowSingleton::GetInstance()->Now();
}

// static
int64 TimeTicks::GetQPCDriftMicroseconds() {
  return HighResNowSingleton::GetInstance()->GetQPCDriftMicroseconds();
}

// static
bool TimeTicks::IsHighResClockWorking() {
  return HighResNowSingleton::GetInstance()->IsUsingHighResClock();
}
